Current low K (dielectric) barrier films cannot meet all the desired requirements, especially low K, high density, Cu diffusion barrier property, O2 diffusion barrier property.
In the microelectronics industry, pattern density shrinks have enabled significant performance gains and continue to occur in the predictable 2 year cycle according to Moore's Law. In order to maintain or improve the operations of a device, both transistor and interconnect level changes have been made. More specifically focusing on the interconnect structures (commonly referred to as the back-end-of line, BEOL), the dimensional shrink has caused a transition from aluminum to copper metallization in order to maintain tolerable line resistances. In order to maintain adequate capacitance between copper lines, the dielectric or insulating films that enclose the copper lines have also changed to compensate for the integration changes necessary for the patterning changes. In order to minimize capacitance of the insulating films, the dielectric constant of each dielectric should ideally be continually reduced. For the interlevel dielectrics (“ILD”), this transition has continually occurred from silicon dioxide to fluorosilicate glass to dense organosilicate glass and finally to porous organosilicate glass with k values of 4.0, 3.3-3.7, 2.7-3.1, and <2.6, respectively.
Typically, the ILD insulating films can retain moisture and O2 in the dielectrics. Given that copper is susceptible to rapid oxidation that can cause reliability issues, barrier dielectrics comprise a portion of the dielectric stack to serve as a diffusion barrier between the copper lines and ILD films, preventing diffusion of water and O2 from the ILD onto the copper surface and preventing copper diffusion into the ILD films. Contrary to the trends for ILD films, the barrier dielectrics have not scaled significantly, due to the reliability functions that the dielectrics serve within the interconnect structure. However, given the disproportionate scaling in dielectric constant of the ILD films relative to the barrier dielectrics, the capacitance contribution of the barriers now is more significant to the overall capacitance of the interconnect structure than in previous technology nodes.
Other semiconductor applications, such as photovoltaics and thin-film display devices, also have requirements for lower k value dielectric barrier films. In addition, the ability to tune the dielectric properties for density, refractive index, film composition and electrical properties is important for extendibility.
Within the current generation of ILD materials, an additional ultraviolet curing step is needed after deposition. Given that the barrier films may exist below the low k ILD films, current generation of barrier films tend to acquire tensile stresses, which further contribute to cracking and deformation of BEOL interconnects. The current industry standard precursors, 3MS (trimethylsilane) or 4MS (tetramethylsilane), cannot meet all the requirements, especially the ability to lower the K values, while maintaining barrier properties. Patents relevant to this field in general include:
US 2008/0197513; US 2008/0173985; US 2008/0099918; U.S. Pat. No. 7,129,187; U.S. Pat. No. 6,500,772; U.S. Pat. No. 7,049,200; U.S. Pat. No. 7,259,050; and U.S. Pat. No. 6,153,261.
In this invention in at least one embodiment, plasma enhanced chemical vapor deposition (PECVD) processes with aminosilane precursors specified below provide dielectric films with dielectric constants that are comparable or lower than current barrier dielectric films while still maintaining adequate barrier properties. These properties include high density, hermeticity and thermal stability.